The invention relates to processes for removing and degrading organic contaminants from liquid or solid phase wastes such as wastewaters, soils, sediments and sludges. More particularly, the invention relates to processes for removing organic contaminants by solvent extraction techniques and degrading the contaminants by photodegradation techniques.
Wastewaters and contaminated soils or solids exist in ever increasing quantities. Chemical producers, pulp and paper plants, oil refineries and sewage treatment plants, for example, produce wastewaters containing toxic and hazardous organic contaminants. Contaminated soils and sediments result, for example, from accidental spills or leakages from underground storage tanks and pipelines as well as from manufacturing plant and transport accidents above ground. Also, land fill or disposal sites containing industrial wastes in storage drums can produce contaminated soils due to leakage. In these instances, the contaminants can also percolate through soils and sediments to contaminate ground water tables and aquifers.
Known treatments for contaminated liquid phase wastes, usually contaminated ground waters or wastewaters, include activated carbon absorption, incineration, packed bed aeration and chemical treatments including ozone or ozone/U.V. irradiation treatments. In many cases, the contaminant is merely transferred from one medium to another and is not removed or eliminated from the environment. Carbon absorption has the disadvantage of having to be replaced or to regenerate the carbon when it reaches its absorptive capacity. Chemical treatments are not available for a large variety of organic contaminants and can be prohibitively expensive. Also, in many instances ozone or ozone/U.V. irradiation techniques practised directly with wastewaters are too expensive or ineffective because large quantities of other compounds in the water can interfere with the photodegradation of a specific toxic organic contaminant targeted for removal. Incineration is only cost effective for very concentrated wastes and frequently results in pollutant emissions to the atmosphere. The packed bed aeration technique is only effective for highly volatile contaminants.
Treatments available for soils, sediments or sludges include incineration, pyrolysis, nucleophilic substitution for chlorinated compounds with such reagents as KPEG or APEG, solvent extraction of specific contaminants followed by carbon absorption or incineration, supercritical oxidation, and in-situ vitrification. Such treatments are expensive and, in some cases, such as the KPEG reagent, are limited to one specific class of compounds. Other of the treatments result in secondary waste disposal problems.
A review of a number of specific proposed waste treatment processes exemplify the limitations and shortcomings of many waste treatment techniques. In an article by M. Pat Esposito, Treatment Technologies for Dioxin Wastes, Proceedings of the National Conference of Hazardous Wastes and Hazardous Materials, Washington D.C., March 1987, treatment techniques for dioxin wastes are reviewed. One system developed by Syntex Agribusiness and IT Enviroscience utilizes solvent extraction and photolysis. The dioxin is extracted from sludge with a hexane solvent and the extract is then irradiated with U.V. light. A major disadvantage of such a process is that the solvent itself, being hydrocarbon in composition, is subject to photodegradation along with the targeted dioxin contaminant, thereby increasing the solvent costs and lowering the effectiveness of the photolysis process.
A technique proposed for the treatment of PCB contaminated solids was described by W. Steiner et al, Low Energy Process Technology for Extraction of PCB from Contaminated Sediment and Sludges at the International Congress on Hazardous Materials Management, Chattanooga, Tenn., June 1987. The process involves leaching the PCB from solids such as soil with a hydrophilic solvent such as acetone, transferring and concentrating the PCBs to a hydrophobic solvent such as kerosene and destroying the PCBs in the solvent stream either by known chemical means, such as with the KPEG reagent or by incineration. Because of the solvent losses in the destruction stages, the process is only cost effective if the contaminant is concentrated in the solvent.
Concentrated organic wastewaters may also be treated by high temperature oxidative techniques. One such process is described by D. Bhattacharyya et al., Oxidation of Hazardous Organics in a Two-Phase Fluorocarbon-Water System, Hazardous Waste & Hazardous Materials, Vol. 3, 1986, 405-427. In this process, wet air oxidation of contaminants in two phases, an aqueous phase which contains organic solutes and a non-polar, inert organic fluorocarbon phase which is presaturated with oxygen, is proposed. In general, wet air oxidation techniques suffer the disadvantages of needing concentrated wastes and high temperatures and pressures.
There is, therefore, a need for a process for the removal and destruction of toxic or hazardous organic contaminants from solid or liquid phase wastes which overcomes the above-described difficulties. Particularly, a process is desired which avoids the consumption or destruction of costly solvents or the use of incineration, high temperature oxidation, or costly chemical reagents in the contaminant destruction stages, and which does not significantly contribute to secondary waste disposal problems, and which also makes on site destruction of contaminants feasible.